title: Oxidative stress in breath-hold divers after repetitive dives.
abstract: BACKGROUND
  Hyperoxia causes oxidative stress. Breath-hold diving is associated with transient hyperoxia followed by hypoxia and a build-up of carbon dioxide (CO₂), chest-wall compression and significant haemodynamic changes. This study analyses variations in plasma oxidative stress markers after a series of repetitive breath-hold dives.
  
  
  METHODS
  Thirteen breath-hold divers were asked to perform repetitive breath-hold dives to 20 metres' depth to a cumulative breath-hold time of approximately 20 minutes over an hour in the open sea. Plasma nitric oxide (NO), peroxinitrites (ONOO⁻) and thiols (R-SH) were measured before and after the dive sequence.
  
  
  RESULTS
  Circulating NO significantly increased after successive breath-hold dives (169.1 ± 58.26% of pre-dive values; P = 0.0002). Peroxinitrites doubled after the dives (207.2 ± 78.31% of pre-dive values; P = 0.0012). Thiols were significantly reduced (69.88 ± 19.23% of pre-dive values; P = 0.0002).
  
  
  CONCLUSIONS
  NO may be produced by physical effort during breath-hold diving. Physical exercise, the transient hyperoxia followed by hypoxia and CO₂ accumulation would all contribute to the increased levels of superoxide anions (O₂²⁻). Since interaction of O₂²⁻ with NO forms ONOO⁻, this reaction is favoured and the production of thiol groups is reduced. Oxidative stress is, thus, present in breath-hold diving.
authors.affiliation: Haute Ecole Paul-Henri Spaak, Environmental and Occupational Physiology Lab., Brussels, Belgium. sigtheunissen@gmail.com
authors.forename: Sigrid
authors.initials: S
authors.lastname: Theunissen
authors.forename: Nicola
authors.initials: N
authors.lastname: Sponsiello
authors.forename: Miroslav
authors.initials: M
authors.lastname: Rozloznik
authors.forename: Peter
authors.initials: P
authors.lastname: Germonpré
authors.forename: François
authors.initials: F
authors.lastname: Guerrero
authors.forename: Danilo
authors.initials: D
authors.lastname: Cialoni
authors.forename: Constantino
authors.initials: C
authors.lastname: Balestra
mesh_terms: D000328:Adult; D015415:Biomarkers / Q000097:blood; D062485:Breath Holding; D004242:Diving / Q000502:physiology*; D006801:Humans; D018496:Hyperoxia / Q000097:blood; D000860:Hypoxia / Q000097:blood; D008297:Male; D009569:Nitric Oxide / Q000097:blood; D009573:Nitrites / Q000097:blood; D018384:Oxidative Stress / Q000502:physiology*; D013438:Sulfhydryl Compounds / Q000097:blood; D013997:Time Factors; D014443:Tyrosine / Q000031:analogs & derivatives / Q000097:blood
chemical_list: D015415:Biomarkers; D009573:Nitrites; D013438:Sulfhydryl Compounds; D009569:Nitric Oxide; C002744:3-nitrotyrosine; D014443:Tyrosine
keywords: breath­hold diving; exercise; free radicals; freediving; hyperoxia; nitric oxide